1. Field of the Invention
This invention relates to the immunisation of pigs against swine dysentery, and in particular it relates to a vaccine for the control of this disease.
2. Discussion of Related Art
An anaerobic spirocheate, Treponema hyodysenteriae, has been isolated and identified as the primary aetiological agent of swine dysentery, a mucoid, haemorrhagic diarrhoea of swine that is worldwide in distribution. The organism has a predeliction for the large intestine (colon) of swine where it proliferates, in the presence of other anaerobic bacteria, and produces a mucoid, haemorrhagic to necrotic degeneration of large portions of the large intestine. There is extensive invasion of the epithelia and lamnia propria of the tissue and the spirochaetes are clearly obvious, under light or electron microscopy, aligned along the necrotic tissue.
There is virtually no information available on the immune response of pigs to T.hyodysenteriae infection although it has been demonstrated that pigs that have recovered from swine dysentery are refractory to further challenge.
Several attempts have been made to develop an effective swine dysentery vaccine. U.S. Pat. No. 4,100,272 describes a vaccine comprising chemically killed cells of a virulent (pathogenic) isolate of Treponema hyodysenteriae for parenteral administration, whilst U.S. Pat. No. 4,152,413 describes a similar vaccine comprising killed cells of a virulent isolate for oral adminstration. U.S. Pat. Nos. 4,152,415 and 4,469,672 describe modification of the oral vaccination procedure which include the step of parenterally administering the vaccine prior to the oral administration thereof.
International Publication No. W085/03875 discloses a modified vaccination regime which comprises parenteral administration of a priming dose of a killed vaccine, and at about the same time or thereafter the oral administration of a live, avirulent or non-pathogenic strain of T.hyodysenteriae.
It will be apparent that in these prior vaccination attempts, killed virulent strains of T.hyodysenteriae have been used and the cells have been treated with fixative chemicals such as formaldehyde. In all instances, the killed vaccine has been administered either alone by injection or orally, or by injection in conjunction will; oral administration of a killed virulent strain or a live avirulent strain. The rationale of the oral administration of the avirulent strain is to stimulate the local immunity of the large intestine, and presumably to stimulate an IgA response.